The present invention is related to a broadband data communication system which utilizes a large number of receiving devices positioned over a large angle of space and, more particularly, to a communication link or links provided between a radar target generator which simulates targets for insertion into radars under test and an angle simulation test array which includes a plurality of infrared-to-microwave transponders.
The complexity of modern air defense weapons is such that the test and evaluation thereof can no longer be satisfactorily performed according to traditional techniques of launching missles at target drones. A reasonably complete test of a modern air defense weapon by such traditional techniques may, for example, require expenditures in excess of a billion dollars and require 38 years to complete. Naturally, this has led to the development of new techniques and systems which, for example, allow a superior test program to be performed in less than a year and about 2 percent of the cost of field testing.
One such facility is known as a radar test chamber which is housed in a hemispherical building having a radius greater than 100 feet and extending over approximately 140.degree.. The radar equipment under test is positioned at the zero radius point. The curved section of the hemisphere is known as the angle simulation test array and comprises a plurality of infrared-to-microwave transponders. Such transponders receive two or more beams of infrared (IR) energy, focus them onto a nonlinear diode or mixing crystal with nonlinear characteristics where the difference frequency is obtained, and retransmit the difference frequency back in the general direction of the origination of the IR. Basically, the angle simulation test array memorizes the radar antenna pattern, receives the IR transmissions, and retransmits microwave signals inversely in proportion to the memorized radar transmissions and directly in proportion to the amplitude of the IR difference signals and at the frequency of the difference between the two IR signals. The walls of the radar test chamber are preferably covered with RF anechoic material for absorbing the RF energy radiated by the radar under test and the angle simulation test array, the transponders being positioned as desired amongst the anechoic material.
Electronic operation of the radar test chamber is initiated with the test radar sending out a transmission which, for many radars, comprises a high frequency pulse. The frequencies in such a pulse are often too high for most commonly available signal processing equipment such that it must be heterodyned down to a more easily processed frequency or band of frequencies. The heterodyning is accomplished in what is known as a radar target generator which develops an intermediate frequency (IF) of, for example, 1.5.+-.0.25 GHz., buffers it, and splits it into up to 110 signals for the development of up to 100 simulated radar targets, the remaining signals being utilized to develop simulations of terrain clutter, weather effects, and chaff. The computer controlled radar target simulated signals take into account such factors as range delay, Doppler, range attenuation, target signature, scintillation, and the like.
Other weapons testing systems presently in use utilize approximately 250 to 500 transponder elements in the angle simulation test array. The system for communicating with such an array has been direct by means of thousands of radio frequency switches which are controlled by a computer. The 250 to 500 element test facilities are however designed primarily for the testing and evaluation of missles which inherently have small radar or communication antennas. The problems involved in communicating with the array become much more severe when the test and evaluation of ground based radar is the objective due to their inherently large antennas and very large fields of view. In other words, while 500 array elements may be perfectly suitable for missle testing, some 28,000 array elements are required for radar testing. In the latter instance, direct communication through RF switches is not feasible inasmuch as millions of such computer controlled switches would be required.